
Note that matrices \(\mathcal {A}, \mathcal {B}, \mathcal {C}, \mathcal {D}\)  are affine in \(\tilde{\theta }\) . The following theorem incorporates the QC for \(\tilde{\phi }\)  in the Lyapunov condition to derive the exponential stability condition of the feedback system using the S-Lemma [1]}, [2]}
